lst standalone: make an option to disable output root file for cleaner benchmarking

[slava77]

or use -w 0 to disable. Apparently with -w 0 only metadata is written to a root file.

The problem leading to opening this issue is an observation that during profiling the writeMetaData occasionally hangs (this is the part where git log/history is collected and written to a txt file and then to the root file).